Trifunctional isocyanate trimers



TRIFUNCTIONAL ISOCYAN ATE TRIMERS N Drawing. Application July 10, 1956, Serial No. 596,851

5 Claims. (Cl. 260-248) Thisinvention relates to novel trifunctional isocyanate trimers and more particularly to the trimers of 4-lower alkyl m-phenylene diisocyanate.

In many applications of isocyanates, it would be highly desirable if a polyfunctional isocyanate were available in which the isocyanate groups would .not react under ordinary or room temperature conditions but which would react at somewhat elevated temperatures and that such an isocyanate material would be readily soluble in most reaction media.

This invention has as an object to provide novel polyisocyanate compounds having hindered isocyanate groups which do not react under many conditions. A further object is to provide the trimers of 4-lower alkyl-m-phenylene diisocyanate and a method for the preparation thereof. Other objects will appear hereinafter.

These and other objects are accomplished by the novel trifunctional isocyanate trimers having the formula wherein R is a lower alkyl radical. The preferred process for preparing these trifunctional isocyanate trimers involves treating 4-lower alkyl-m-phenylene diisocyanate with a catalytic amount of tri-n-butyl phosphine. They may also be prepared by treating the 4-lower alkyl-rm phenylene diisocyanate monomer with dimethyl formamide saturated with sodium benzoate. These processes are more particularly illustrated in the following examples. The diisocyanate monomers from which the trimers of the present invention are prepared are well known in the art, with the exception of 4-tert.butyl-mphenylene diisocyanate. This compound is more particularly described and claimed in copending application of Stilmar, U. S. Serial No. 516,035, filed June 16, 1955. 4-tert.butyl-m-phenylene diisocyanate may be prepared by the reduction of the corresponding dinitro compound to the diamine and the subsequent phosgenation of the diamine to produce the diisocyanate.

The novel trimers of the present invention are soluble in methanol, benzene, ethyl acetate, toluene and tetrahydrofuran but insoluble in petroleum ether or octane. This solubility is very advantageous in preparing adhesive formulations and the like. In the preparation of these formulations, it is desirable to have an isocyanate material which will remain stable on storage. With the use of these novel trimers, wherein all three of the -NCO groups are shielded with lower alkyl groups, it

Patent 0 ice is possible to make an adhesive which will remain stable for a matter of days and still have reactive isocyanates which can be utilized when they are heated to a somewhat higher temperature. These isocyanate adhesive formulations can be used to adhere metal to metal, plastic to metal, plastic to plastic, etc. The use of these trimers in adhesive formulations is more particularly described in the examples. The novel trimers of the present invention may also be used as curing agents for elastomers containing active hydrogen atoms.

The following examples will better illustrate the nature of the present invention. Parts are by weight unless otherwise indicated.

Example 1 To 30 parts of 4-tert.butyl-m-phenylene diisocyanate in an agitated vessel is added 0.13 part of tri-n-butyl phosphine. The mixture is thoroughly stirred and then allowed to stand overnight with slow stirring. Some heat of reaction is observed initially and the liquid slowly becomes very viscous. At this stage it is transferred from the vessel into a closed, shallow vessel where it slowly solidifies. The solid product is then broken up and extracted with boiling petroleum ether. The petroleum ether insoluble product which is the trimer is dissolved in 150 parts of ethyl acetate at room temperature and further diluted by the addition of 100 parts of isooctane. The solution thus obtained is evaporated until crystallization begins and then it is cooled. The white crystalline material is filtered ott and washed with a small amount of isooctane. On drying at C., there is obtained 21 parts of the dry product in the form of colorless needles which melt at 3l03l1 C. The product is soluble in ethyl acetate, tetrahydrofuran, benzene, carbon tetrachloride and methyl alcohol but insoluble in petroleum ether or isooctane. Analysis shows 19.1% NCO comparedwith a theory of 19.45%. Infrared absorption curves show the presence only of the trimeric structure and none of the dimeric structure.

Example 2 To 25 parts of 4-tert.butyl-m-phenylene diisocyanate dissolved in parts of dry isooctane is added 0.5 part of tri-n-butyl phosphine. The solution is stirred 3 to 4 hours at room temperature and then allowed to stand for 48 hours. A solid crystalline product separates during this time. It is filtered off, washed with isooctane and dried at 80 C. The yield is 14 parts of the trimer of 4-tert.butyl-m-phenylene diisocyanate melting at 308 311 C. Recrystallization from ethyl acetate and isooctane yields a purified product melting at 3l0-31l C. Infrared spectral analysis shows it to be identical with the product of Example 1.

Example 3 To 15 parts of cumene-2,4-diisocyanate is added 0.5 part of tri-nbutyl phosphine at room temperature and the mixture is stirred well. The temperature rises to about 62 C. and the liquid becomes quite viscous in a short time. After standing without further agitation and at room temperature overnight, a transparent solid mass forms. The mass is broken up, powdered and extracted with boiling petroleum ether to remove any unreacted diisocyanate and the catalyst. 13.6 parts of a white powder is obtained which melts at 346350 C. Infrared analysis shows the trimer structure characteristic of Example 1 with only a trace of dimer structure. The trimer is soluble in ethyl acetate, carbon tetrachloride, benzene and tetrahydrofuran.

Example 4 To 15 parts of 4-sec.butyl-m-phenylene diisocyanate is added 0.5 part.of tri-n-butyl phosphine with stirring at room temperature. The reaction is exothermic and the temperature rises to about 57 C. and the liquid becomes viscous. After standing overnight at room temperature, a clear, brittle solid is obtained. It is broken up and extracted with boiling petroleum ether. 13.3 parts of a White powder, melting at 364 367 C., is obtained. Infrared analysis shows it to be the trimer and it is soluble in ethyl acetate, carbon tetrachloride, benzene and tetrahydrofuran.

The trimers of 4-methyl-m-phenylene diisocyanate and 4-ethyl-m-phenylene diisocyanate may be prepared in a manner similar to that used to prepare the trimers in Examples 1 to 4.

Example To 122 parts of toluene-2,4-diisocyanate is added 2 parts of dimethyl formamide saturated with sodium benzoate with stirring at room temperature. The temperature rises to about 40 C. and the mixture thickens. After necessary to rupture the bond. These are averages of 3 samples. The tests are made on an Instron testing machine.

7 Length of cure, hours 1 5 5 Temperature of cure, C 120 120 190 Lbs. to rupture bond 228 668 772 Average bond strength, 1bs./sq. in 456 1,336 1, 544

standing overnight at room temperature, a semi-crystal- To 12 parts of cumene-2,4-diisocyanate at room temperature is added about 0.2 part of dimethyl form-amide saturated with sodium benzoate. The temperature is maintained at -30 C. with slight cooling for 4 hours. The viscous mass is dissolved in anhydrous ether and then poured into petroleum ether to precipitate the trimer. The trimer is filtered oif and dried. 6 parts of a white powder is obtained showing the characteristic trimer band by infrared analysis.

Example 7 An adhesive formulation is made by mixing 2 parts of,

methylethyl ketone, 3 parts of the trimer of 4-tert.butylm-phenylene diisocyanate and 1.1 parts of a polyester prepared by heating and stirring together 438 parts of adipic Q acid, 248 parts of ethylene glycol, 92 parts of glycerine, and 148 parts of phthalic anhydride for 16 hours at 175 C. while passing a slow stream of nitrogen through the As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

This application is a continuation-in-part of copending application Serial No. 516,034, filed June 16, 1955, now abandoned.

What is claimed is:

1. Isocyanate trimers having the formula N00 I NCO wherein R is a lower alkyl radical.

2. The trimer of claim 1 wherein the Rs are tertiary butyl radicals.

3. The trimer of claim 1 wherein the Rs are secondary butyl radicals.

4. The trimer of claim 1 wherein the Rs are isopropyl radicals.

5. The trimer of claim 1 wherein the Rs are methyl radicals.

No references cited. 

1. ISOCYANATE TRIMERS HAVING THE FORMULA 